How do I pixelize this light screen?
While I am not familiar with the subject in question, one way would be to use a custom image and use it as an emissive shader. 

image used: http://orig14.deviantart.net/3961/f/2012/050/a/f/wheatley__s_eye_by_mycroftporthos-d4qarjf.png 

Obviously you can find a better image (more pixelated) or make your own and use some filter in photo editors app like Photoshop, Affinity, Gimp or whichever you prefer.
Photoshop has a bunch of filter under the category Pixelate.
Affinity also has a filter under the Distort category called Pixelate and I'm sure Gimp also has one.